main()
{
    int a=21,i;
    printf("Game begain:\n");
    while(a>0){
    do
      {
          printf(" How many sticks do you wish to take (1~%d) ? ",a>4 ? 4: a);
          scanf("%d",&i);   
      }
   while (i>4 || i<1 || i>a );
    if (a-i>0) printf(" %d sticks left in the pile.\n",a-i);
    if ((a-i)<=0)
    {
        printf(" You have taken the last sticks. \n");
        printf(" * * * You lose! \nGame Over.\n");
        break;
    }
    else  
      printf(" Computer take %d sticks .\n",5-i);
    a-= 5;
      printf(" %d sticks left in the pile. \n",a);
    }
}